Researchers found that 37 percent of children had two hours or less of recreational screen time per day, 51 percent had 9 to 11 hours of uninterrupted sleep per night, and 18 percent got at least 60 minutes per day of moderate to vigorous physical activity.

Only 5 percent of the children in the study met all three recommendations. Twenty-nine percent met none at all.

Researchers found that children who met the guidelines for all three areas had “superior global cognition” compared to those who met none. This includes memory, attention, processing speed, and language.

The strongest link was for screen time alone, and for screen time and sleep together.

The researchers did not see a connection between physical activity and improved cognition. However, they noted in the paper that this may be due to a lack of information about the intensity and kinds of physical activity that kids were doing.

While there are guidelines for healthy levels of screen time, sleep, and physical activity for children, this study looked at how they interacted.

Heather Kirkorian, PhD, an associate professor in human development and family studies at the University of Wisconsin–Madison, who as not involved in the study, said one of the strengths of the study is that researchers measured cognitive abilities directly rather than relying on a parent’s assessment.

Kirkorian pointed out, though, that the results only show some association between these factors, but they can’t say which one causes which.

This is echoed by Chaput, who said, “We know that screen time before bed is bad for your sleep quality, but we also know that short sleepers tend to engage in more screen time.”

Another recent study found a similar impact of screen time, sleep, and physical activity — along with diet — on the academic performance of more than 4,000 10- and 11-year-olds.

Kids in this study who met the screen time and sleep recommendations performed better on a standardized writing test taken one year later.

But math, reading, and writing all improved with each additional good lifestyle behavior that children had.

Study author Paul Veugelers, PhD, a professor of public health at the University of Alberta said the effect of these lifestyle behaviors on academic performance was “substantial.”

This study looked only at television viewing, which may capture just a small piece of children’s screen time.

Also, Veugelers said that asking kids how often they use screens may miss information about their other health habits.

“Hypothetically you can have a student playing with the Wii or Dance Revolution and reporting that as screen time,” he said.

Kirkorian would like to see additional research that gives a more detailed view of screen time.

“There’s plenty of research suggesting that the type of activity, the content, and the social context all matter,” she said.

For example, there’s a difference between watching a movie alone or watching and talking about the movie with others, or between playing video games and doing research online for school.

The AAP recommends that parents limit screen time to less than two hours for children age 5 or under. But they are more flexible for older children and teenagers, focusing more on screen-time activities rather than setting time limits.

“Parents should be aware of what their kids are doing and talk to them about it,” said Kirkorian. “But the guidelines don’t necessarily say parents should be there for every minute of screen time.”

Veugelers said it’s not just the parents’ responsibility to help children learn healthy habits for screen use, eating, physical activity, and sleep. The schools, school boards, teachers, and communities should be involved, too.

Both of these studies emphasize that screen time is just one factor affecting children’s cognitive abilities.

So parents should keep the whole day in mind when helping their child develop good habits.

“Start your day with a good night’s sleep, try to move as much as possible, and try to limit your sitting time or screen time,” said Chaput. “This is going to be good not just for your health, but also for your cognitive function. And for kids, if they have better cognitive function, they may succeed better in their life.”

Researchers found that children who had less than 2 hours of screen time, had enough sleep, and got a recommended amount of physical exercise had “superior global cognition” compared to those who did not have these lifestyle habits.

This improved cognition includes memory, attention, processing speed, and language.